HOW do you get inside an animal's head and assess how it's feeling? The short answer is, you can't. But a study on starlings has taken us one step nearer by revealing how animals change their behaviour in response to different environmental conditions.
The information could improve our understanding of animal welfare.

Melissa Bateson and colleagues at Newcastle University, UK, investigated how starlings respond to different living conditions, by giving them choices designed to assess whether their outlook was "pessimistic" or "optimistic".

Birds were trained to associate a tasty snack - a worm - with a dish with a white lid, and an unpalatable quinine-flavoured worm with a dish with a dark grey lid. Starlings soon learned not to bother flipping open dark grey lids.

The birds were then kept either in "enriched" cages with branches and water baths, designed to promote greater welfare, or in standard cages that were smaller and bare.

Next, the birds were given dishes with lids of various intermediate shades of grey. When there was ambiguity over the colour, and thus whether there was a tasty snack inside, only those birds kept in the enriched cages were likely to bother flipping open the lids.
In other words, starlings in enriched cages were more "optimistic". The results will appear in Animal Welfare.

In another experiment designed to test their feelings, starlings learned to discriminate between light signals that indicated either an instant or a delayed food reward, and act upon them accordingly.
When the signals were ambiguous, those in standard cages were "pessimistic" in their response (Applied Animal Behaviour Science, DOI: 10.1016/j.applanim.2007.03.07). Experiments by a team at the University of Bristol, UK, have shown similar results in rats.

"If you have information coming in that the environment is a bad place, then it makes sense to make adaptive changes to the way you process information," says Bateson.
This is why our reaction times tend to go down when we are anxious, or we are more likely to interpret an ambiguous shadow as a spider.

Until now, farmers have had to wait for obvious signs - such as sores on chickens' legs - before they could tell that there was a problem.

"We're not getting into animals' subjective experience, but it's important to look as deeply as possible at the levels at which we are similar to animals," says Bateson. "We can't improve animal welfare unless we have ways of assessing their emotional states."

Veterinary scientist John Bradshaw of the University of Bristol says that switches from optimism to pessimism in humans can be associated with the onset of depression. "It is possible that the same changes in non-human animals are also associated with mood changes."